Where to find Presentations & Handouts

There’s now a link over in the Useful Stuff section that’ll take you to my presentation files & handouts.

Sherline Mill Counterweight Gantry: Center Support

Expanding plug on crossbeam
Expanding plug on crossbeam

This is the dingus that attaches the crossbeam to the central pipe rising up from the table for my counterweight gantry. I discarded a whole bunch of elaborate construction ideas in favor of just jamming a plug in the pipe and cranking down on a nut to tighten it.

Expanding plug overview
Expanding plug overview

It’s pretty much self-explanatory; I cut everything to fit, cleaned up the cuts with a file, and added some lube to the tapers so as to make it nice & slippery.

The need for an O-ring to hold the halves together occurred to me after I’d bandsawed a 1 mm trench in the side of the plug. I chucked it up in the lathe again and used a round-nose tool to carve a groove around its belly. If you try this, do the groove first: an interrupted cut is murder on what’s basically a parting-off tool.

Expanding plug parts
Expanding plug parts

While I know (thanks to Guy Lautard’s invaluable Machinist’s Bedside Reader books) that a self-releasing plug must have a taper angle with a tangent greater than the joint’s coefficient of friction, that really wasn’t much help here. I picked 40 degrees and, yup, it’s self-releasing, but not really slippery enough. Takes a bit of torque to expand the plug enough for a good grip.

Perhaps my grubby surface finish has something to do with it?

Memo to self: find out how to figure the taper angle correctly, then do better finishing.